The role of nutrition in reproduction
Madison - Over the past few years, there have been dramatic improvements in dairy reproductive performance.
Research is revealing and the industry is embracing aspects of management, genetics and physiology that are propelling repro rates, Dr. Milo Wiltbank, University of Wisconsin Madison dairy scientist, said during the March DAIReXNET webinar.
Cow comfort, compliance and AI skills are essential for productive management, he noted. Genomics now allow selection of cows that are higher for DPR (daughter pregnancy rate) and cow conception rate, and reproductive management programs are available that drive service rate and improve fertility.
But when it comes to high-efficiency dairy cattle and reproduction, Wiltbank said, nutrition is a particularly big player.
The role of nutrition
Recent research has illuminated the important time periods to focus on and the effect of Vitamin E on reproductive performance, as well as the importance of dry period nutrition and postpartum body condition score.
Wiltbank splits a cow's timeline into several critical segments: the dry period of the last three weeks before she calves, the early post-partum of three weeks following calving, and the pre-AI period of one week before breeding.
Vitamin E plays a critical role in cow health. It decreases as calving approaches due to accumulation in colostrum, which poses problems since cows with lower levels are more likely to retain fetal membranes.
Wiltbank reported that research geared toward improving retained placenta rates was conducted on three dairy farms in Brazil. There were nearly 900 cows in the study that injected 1,000 IU of vitamin E at three weeks, two weeks and one week before expected calving.
While the amount of vitamin E injected was not enough to change concentrations, it was enough to have an impact on outcomes. Retained placenta rates dropped significantly, from 20 percent in the control group to 13.5 percent in the Vitamin E group.
Interestingly, stillbirths were dramatically reduced by supplementing Vitamin E, dropping from nearly 15 percent to under 9 percent. "This suggests that stillbirth is also related, probably to the placenta, and probably to the Vitamin E and immune status of the animal," Wiltbank said. "This was an intriguing result."
There was no effect on milk production, but reproductive performance also improved. Pregnancy losses for first postpartum AI dropped significantly with Vitamin E , while the percentage of cows pregnant from all AIs was significantly higher with the vitamin.
"That was a key result", Wiltbank observed. "Somehow, by supplementing Vitamin E before calving, we can reduce retained placentas, stillbirths and pregnancy losses, and also somewhat improved fertility."
Another study focused on how prepartum nutritional strategy affects reproductive performance by evaluating seven previous studies. The effort involved over 400 cows fed controlled energy or high energy diets during the far-off or close-up dry period.
Nutrition had no effect on the far-off dry period, but it did close-up. With the controlled energy diet, the period from calving to pregnancy were reduced by 10 days and body condition score (BCS) losses were reduced.
"There was better reproductive performance when we had a more controlled energy, a higher fiber, diet during the dry period," Wiltbank pointed out.
The studies make the argument that reproductive performance can be improved by optimizing nutrition during the dry period. "Dry period nutrition can alter calving and early postpartum physiology and subsequent fertility," he summarized.
In recent years, researchers have tested whether nutrition in early postpartum has an effect on embryo quality. Wiltbank referenced a study on the relationships between fertility and postpartum changes in body condition and body weight in lactating dairy cows, showing a cow's body condition score at the time of AI does, indeed, impact her fertility.
In one experiment involving double-Ovsynch for first service and over 1,880 cows in Wisconsin, researchers evaluated BCS at calving and 21 days later. About 42 percent of the cows lost BCS, 36 percent maintained BCS and over 22 percent actually gained BCS.
"The effect on fertility was just incredible," Wiltbank said. "The animals that gained weight had amazing fertility, and it dropped down from there."
At 40 days, cows that lost BCS had 25 percent fertility, while cows that maintained BCS had 38 percent and cows that gained BCS hit 84 percent fertility. Subsequent studies echo the results, Wiltbank noted.
Research on embryo quality was also conducted by weighing the animals weekly after calving, superovulating them and then evaluating the embryos to determine the effects of body weight changes.
The study of 460 embryos found big differences. Almost 50 percent of the low BCS animals had degenerate embryos, compared to 20 percent in other weight groups. "There was quite a dramatic difference, and it was mostly for the animals that lost a lot of body weight (about 8 percent) in the early post-partum period," Wiltbank said.
He noted that lower BCS near the time of AI reduces fertility, but this effect might be addressed by Double-Ovsynch protocol.
Considering the last week before AI is a very sensitive period, researchers tried to evaluate how dietary components are associated with fertility traits. Complete diets were obtained on 50 dairy farms with Dairy Comp 305 backups for fertility and other traits.
The resulting data showed the higher the non-detergent fiber in the diet, the better the pregnancy rate at first AI, but the higher the non-fiber carbohydrate, the lower the pregnancy rate per AI at first service. "The high carbohydrate seems to be very much a negative. The same is true for starch," Wiltbank observed.
Too high of carbohydrates in diets reduces pregnancies per AI, possibly due to elevated insulin in the blood, he summarized, while fat, particularly polyunsaturated fatty acids, can improve pregnancies per AI.
Methionine in the diet has been shown to improve reproductive efficiency by stopping abnormal gene expression. "It seems to have a effect on pregnancy loss with multiparous cows," Wiltbank said, noting pertinent research is ongoing.
Wrapping it up
Considering the critical periods for nutritional effects on reproduction, Wiltbank offered four keys. Improve nutrition in the dry period, particularly in terms of sufficient Vitamin E and energy.
In early post-partum, reduce BCS loss to positively impact the embryo.
One week before AI, Improve nutrition by lowering the NFC and increasing PUFA to impact fertility and, during pregnancy, optimize amino acids to reduce pregnancy losses.